AFAIK, the issue is the leads and human heart tissue. Cardiac tissue is partially conductive (conceptually, there are embedded, invisible, conductive channels).

It's not like skin, where you can re-implant into scar tissue or re-implant very close to another implantation location. The signal won't carry through the scar tissue. The lead wearing out (and coming out) comes with commensurate tissue scarring in an area. After a few implantations, you don't have a location that will carry the signal, reliably, as if it was natural cardiac tissue.

You want to replace/repair as few times as possible, to extend the utility of a pace-maker.